For packaging materials for foodstuffs, etc., greaseproof paper with grease resistance imparted thereto is widely used. The greaseproof paper is defined as “1) a collective designation of a paper having oil resistance, and 2) a paper or board which is extremely resistant to permeation of grease or fats.” in JIS-P0001 (1998) “Paper, board and pulp—Vocabulary”. Greaseproof paper is used for packaging a foodstuff, which contains a large amount of oil or a grease component, such as chocolate, pizza and a doughnut, in order to prevent grease from permeating a packaging material. This is because, if oil or a grease component contained in a foodstuff permeates a packaging material, grease may reach a surface not in contact with the foodstuff, resulting in a grease stain which may: deteriorate appearance and thus reduce a commercial value; darken a printed part and thus reduce readability of printed characters; and deteriorate OCR suitability of a bar code or the like. Furthermore, since grease may transfer to clothes and cause a problem of stain and the like, greaseproof paper in which grease resistance has been imparted to a portion to be in contact with a foodstuff is used.
Conventionally, a fluorine compound, particularly a perfluoro fluorine compound has been used as a greaseproofing agent for developing grease resistance of greaseproof paper. Unlike non-fluorine-type greaseproof paper such as glassine paper, parchment paper, coated paper and laminated paper, or a plastic film, fluorine-type greaseproof paper provides superior water resistance and grease resistance while providing breathability (particularly water vapor permeability), and thus has been suitably used for packaging of a foodstuff such as deep-fried food that requires prevention of humidity accumulating inside a package, and for packaging a freshness preservative or a deoxidant that functionally requires breathability.
Among methods of water proofing and grease proofing of paper, in an additive processing method in which a paper substrate is impregnated or coated with a processing agent, a size press or various types of coaters are used; and a copolymer of vinylidene chloride with a (meth)acrylate having a polyfluoroalkyl group has been proposed. However, a short immersion time period may result in problems of insufficient adsorption to the paper and in turn inferior water resistance and grease resistance, and of reduced water resistance of the paper due to inferior water resistance.
In order to develop superior grease resistance and superior water resistance, a water repellent and oil resistant composition has been proposed which contains a specific cationic fluorine-based greaseproofing agent, a non-fluorine surfactant, a medium, and a water-soluble polymer selected from a polyacrylamide, polyvinyl alcohol and starch as essential components (refer to Patent Document 1).
Furthermore, in recent years, it has been revealed in connection with fluorine compounds having a perfluoroalkyl group that: perfluorooctane sulfonic acids generated during a fluorine compound production process in an electrolytic polymerization method accumulate widely in environment such as blood of humans and animals, and marine water; and a fluorine compound produced by an electrolytic polymerization method or a telomerization method generates a perfluoroalcohol that is highly environmentally accumulative, due to heating at 100° C. or higher, regardless of the production method. A carbon number of the perfluoroalkyl group is therefore recommended to be less than 8. In this respect, instead of the conventional fluorine-based greaseproofing agent, a novel alternative fluorine-based greaseproofing agent has been proposed, obtained by employing a short perfluoroalkyl group having 6 or less carbon atoms, or a polyfluoropolyether (refer to Patent Document 2).
However, in the case of using for greaseproofing of paper, the environmentally conscious greaseproofing agent as disclosed in Patent Document 2, in which a carbon chain length of the perfluoroalkyl group is 6 or less, is less likely to attain sufficient grease resistance, and thus a large amount of the greaseproofing agent may be required for obtaining desired grease resistance. Therefore, sufficient grease resistance may not be imparted to, for example, thin paper of low grammage, and cardboard with a greaseproof paper layer of low grammage.